5-HT2C receptor binding is increased in the substantia nigra pars reticulata in Parkinson's disease.

The involvement of abnormalities in nondopaminergic transmitter systems in Parkinson's disease is noteworthy because of the complications, such as dyskinesia, associated with long-term dopamine replacement therapy. The output regions of the basal ganglia, the substantia nigra pars reticulata, and the medial segment of the globus pallidus are overactive in Parkinson's disease but underactive in dyskinesia. 5-HT2C receptors are localized in these regions and are excitatory. A 5-HT2C receptor binding assay using [3H]-mesulergine and SB 200646A to define nonspecific binding was applied to postmortem tissue from patients with Parkinson's disease and from age-matched control patients. [3H]-mesulergine binding was increased in the substantia nigra pars reticulata by 108% in Parkinson's disease tissue as compared with control tissue. These data suggest abnormalities of 5-HT2C transmission in the basal ganglia of patients with Parkinson's disease.